AFOS product AFDCHS
Dates interpreted at 00:00 UTC

Displaying AFOS PIL: AFDCHS
Product Timestamp: 2013-12-27 11:48 UTC

Download date range (UTC midnight)
Bulk Download Bulk Download
022 
FXUS62 KCHS 271148
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
648 AM EST FRI DEC 27 2013

.SYNOPSIS...
A LARGE RIDGE OF HIGH PRESSURE WILL REMAIN SITUATED JUST NORTH OF
THE REGION INTO TONIGHT. LOW PRESSURE WILL DEVELOP IN THE GULF OF
MEXICO SATURDAY AND TRACK NORTHEAST OVER OR NEAR THE AREA THROUGH
EARLY SUNDAY...BRINGING A PERIOD OF WET WEATHER TO SOUTHERN SC
AND SOUTHEAST GA THIS WEEKEND. A WEAK COLD FRONT WILL MOVE THROUGH
MONDAY NIGHT...FOLLOWED BY HIGH PRESSURE WHICH WILL LINGER THROUGH
THE LATTER PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
TODAY...A DAMPENING AND FAST-MOVING SHORT WAVE TROUGH WILL PROGRESS 
FROM THE EASTERN GREAT LAKES AND OHIO VALLEY EARLY ON TO THE 
MID-ATLANTIC REGION AND NEW ENGLAND FOR THE AFTERNOON. AS THIS 
OCCURS IT ALLOWS FOR A DEEP-LAYERED SW ATLANTIC RIDGE TO POKE A 
LITTLE NORTH AND NW ATOP THE LOCAL AREA. SIMULTANEOUSLY THIS KEEPS 
AN EXPANSIVE SURFACE RIDGE IN PLACE OVER A GOOD PORTION OF THE 
EASTERN HALF OF THE COUNTRY. THIS IN TURN BLOCKS A NOTICEABLE
BAROCLINIC ZONE WITH A CONSTANT FEED OF SUB-TROPICAL MOISTURE NOT
TOO FAR OFF TO THE SE AND SOUTH.

WE/LL BE LOCATED WITHIN THE ANTICYCLONIC INFLUENCES OF THE BLOCKING 
SURFACE HIGH...WHICH WILL KEEP THE BEST LOW LEVEL CONVERGENCE JUST 
OUTSIDE THE CWFA TO THE SOUTH. THERE ARE HOWEVER A FEW WEAK MID
LEVEL IMPULSES THAT WILL TRAVEL BRISKLY THROUGH THE SW AND WEST
FLOW ALOFT THAT WILL SKIRT OUR SOUTHERNMOST ZONES. SO A FEW
SHOWERS COULD SNEAK NORTH ACROSS THE ALTAMAHA RIVER THIS
AFTERNOON...AND/OR THE LOW LEVEL FLOW MAY VEER A LITTLE FURTHER
EAST THAN IS NOW ANTICIPATED. THIS WOULD ENHANCE LOW LEVEL
CONVERGENCE FROM OFF THE ATLANTIC...PERHAPS GENERATING ISOLATED
SHOWERS. FOR NOW WE HAVE HELD POPS TO LESS THAN 15 PERCENT...THUS
NO MENTION OF SHOWERS IN THE ACTUAL FORECAST PRODUCTS.

SKY COVER AND THE RESULTING TEMPERATURE FORECAST WILL BE THE TWO
MAIN FORECAST CHALLENGES TODAY. WHILE VARYING AMOUNTS OF JET
INDUCED MID/HIGH LEVEL CLOUDS WILL FILTER THE SUNSHINE AT TIMES
OVER NORTHERN AND CENTRAL ZONES...THE MORE OPAQUE STRATOCUMULUS
CLOUDS WILL RESIDE OVER SOUTHERN COMMUNITIES. THIS LOOKS TO BE
APPROXIMATELY SOUTH OF A LINE FROM ABOUT HILTON HEAD TO
SPRINGFIELD...CLAXTON AND REIDSVILLE. ANY FLUCTUATION NORTH OR
SOUTH WITH THIS THICKER CLOUD COVER WILL HAVE AN IMPACT ON OUR MAX
TEMPS. SO TODAY MIGHT BE ONE OF THOSE RARE DAYS WHEN IT/S ACTUALLY
WARMER NORTH THAN SOUTH DEPENDING UPON HOW SKY COVER TRENDS PAN
OUT. FOR NOW WE HAVE SHOWN UNIFORM TEMPS EVERYWHERE...BUT AT
LEVELS NEAR OR SLIGHTLY BELOW CLIMATOLOGICAL NORMALS WITHIN A
NORTH AND NE SYNOPTIC FLOW.

TONIGHT...RIDGING ALOFT AND THE SURFACE HIGH TO THE NORTH WILL 
PERSIST...WHICH HOLDS OFF ON ANY NORTHERN PROGRESSION OF THE
BAROCLINIC ZONE UNTIL CLOSER TO DAYBREAK SATURDAY. WE/LL BE
CLOSELY WATCHING A SHORT WAVE ARRIVING IN THE GULF OF MEXICO FROM
THE BAY OF CAMPECHE OVERNIGHT...WHICH ALLOWS FOR WEAK CYCLOGENESIS
LATE IN THE PERIOD. WIND FIELDS LOCALLY IN THE LOWEST LEVELS
ABOVE THE NOCTURNAL INVERSION VEER AROUND TO THE EAST...WHILE A SW
AND WEST FLOW PREVAILS THROUGHOUT MUCH OF THE VERTICAL ABOVE 4-5K
FT. THIS PRODUCES AN INCREASE IN ISENTROPIC UPGLIDE AND ALSO
CAUSES A LITTLE COASTAL CONVERGENCE OVER FAR SE GEORGIA. THAT MAY
BE ENOUGH TO GENERATE ISOLATED SHOWERS AFTER 4 OR 5 AM IN MCINTOSH
AND COASTAL LIBERTY COUNTIES...BUT THE VAST MAJORITY OF THE REGION
WILL BE RAINFREE. A DECENT SPREAD IN CLOUD COVER WILL BE IN
PLACE...WITH SKY COVERAGE RANGING FROM 40-50 PERCENT NW TO 80-90
PERCENT SE. AS WINDS DECOUPLE OVER NW SECTIONS IN CLOSER PROXIMITY
TO THE CENTER OF THE RIDGE TO THE NORTH...MINIMUMS WILL FALL INTO
THE MIDDLE 30S. BUT WITH CONTINUED AIR MASS WARMING OUR TEMPS WILL
TREND HIGHER AS ONE HEADS SE. UPPER 30S AND LOWER 40S WILL BE
COMMON IN THE CORRIDOR FROM MCCLELLANVILLE TO CHARLESTON...
BEAUFORT...SAVANNAH AND CLAXTON. WARMEST WILL BE ALONG THE
IMMEDIATE COASTS OF SC AND THE SE QUADRANT OF GEORGIA WHERE UPPER
40S TO NEAR 50 WILL PREVAIL.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
SATURDAY AND SATURDAY NIGHT...ALOFT THE PATTERN WILL BEGIN TO 
AMPLIFY BETWEEN RIDGING OVER THE BAHAMAS/CARIBBEAN AND A CLOSED 
LOW/SHORTWAVE OVER THE SOUTHERN PLAINS. AS THE SHORTWAVE OVER THE 
SOUTHERN PLAINS AND DEVELOPING JET ENERGY EVOLVE...A WEAK SURFACE 
LOW IS POISED TO DEVELOP OVER THE CENTRAL/NORTHERN GULF OF MEXICO ON 
SATURDAY. THIS LOW IS THEN EXPECTED TO TRACK TO THE NORTHEAST AND 
ACROSS OR JUST INLAND OF THE FORECAST AREA THROUGH THE OVERNIGHT. 
SATURDAY WILL BRING ABOUT A SIGNIFICANT MOISTENING OF THE AREA AS 
DEEP MOISTURE STREAMS IN WITHIN THE DEEP SOUTHWEST FLOW. IN 
FACT...PWATS SURGE TO AROUND 1.75 INCHES LATE SATURDAY NIGHT WHICH 
IS NEAR THE 99TH PERCENTILE FOR LATE DECEMBER. INCREASING ISENTROPIC 
LIFT WILL KICK OFF THE INCREASING POP TREND ON SATURDAY...AND RAIN 
CHANCES INCREASE FROM SOUTH TO NORTH THROUGH THE DAY. THE PRIMARY 
PERIOD OF RAINFALL WILL TAKE PLACE SATURDAY NIGHT INTO SUNDAY 
MORNING AS THE SURFACE LOW DRAWS CLOSER AND DEEPER FORCING INVADES 
FROM THE WEST. PRECEDING THE DEVELOPING LOW...HIGH PRESSURE WILL BE 
POSITIONED JUST TO THE NORTH OF THE AREA SATURDAY MORNING. A CAD 
EVENT WILL BE UNDERWAY...AND WILL LIKELY THEN BE DIABATICALLY 
REINFORCED BY ANY PRECIP THAT OCCURS SATURDAY AFTERNOON EVENING. THE 
QUESTION THEN BECOMES WHAT IS THE EXACT TRACK OF THE LOW AND HOW 
QUICKLY IS THE CAD SCOURED OUT AND REPLACED BY A WARM SECTOR AND 
SOUTHERLY FLOW. THIS HAS SIGNIFICANT IMPLICATIONS FOR 
TEMPERATURES...THUNDERSTORMS...AND ANY SEVERE WEATHER POTENTIAL. THE 
MODELS CONTINUE TO SHOW SIGNIFICANT TRACK/TIMING DIFFERENCES SO 
OVERALL CONFIDENCE IN THE DETAILS IS QUITE LOW. REGARDING THE SEVERE 
WEATHER POTENTIAL...LATE SATURDAY NIGHT A STRENGTHENING WIND FIELD 
WILL SPREAD ACROSS THE REGION. THE MAIN QUESTION WILL BE THE DEGREE 
OF SURFACE DESTABILIZATION...IF ANY...IN WHAT WILL CERTAINLY BE A 
HIGH SHEAR/LOW CAPE ENVIRONMENT. GIVEN THE QUESTIONS SURROUNDING THE 
TRACK AND TIMING OF THE LOW...I WILL NOT MENTION ANYTHING IN THE 
HWO. 

SUNDAY THROUGH MONDAY...THE SURFACE LOW WILL MAKE ITS CLOSEST PASS 
SUNDAY MORNING AND THE FORECAST AREA SHOULD BECOME SOLIDLY WARM 
SECTORED AT SOME POINT. THE BULK OF PRECIP WILL OCCUR IN THE MORNING 
WITH A DIMINISHING TREND IN THE AFTERNOON. CATEGORICAL POPS REMAIN 
IN PLACE SUNDAY MORNING...WITH MUCH OF THE AREA GOING DRY IN THE 
LATE AFTERNOON/EVENING HOURS. THE DAMPENING SHORTWAVE ALOFT WILL 
RAPIDLY MOVE AWAY FROM THE AREA ON SUNDAY THOUGH MEAN TROUGHING WILL 
CONTINUE THROUGH MONDAY. BEFORE THE COLD FRONT PASSES THROUGH ON 
SUNDAY...TEMPS WILL SURGE TO THE UPPER 60S IN MANY AREAS WITHIN THE 
WARM SECTOR. MONDAY WILL THEN BE MORE OF A TRANSITION DAY IN BETWEEN 
THE DEPARTING SURFACE LOW AND ANOTHER MORE SUBTLE COLD FRONT ALONG 
THE LEADING EDGE OF HIGH PRESSURE BUILDING IN FROM THE WEST. MONDAY 
WILL BE DRY AS THE ANOMALOUSLY HIGH PWATS DIMINISH BACK TO AROUND 
0.5 INCHES. TEMPS WILL COOL BACK CLOSER TO CLIMO WITH HIGHS IN THE 
LOW 60S EXPECTED.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
OVERALL...THE LONG TERM PERIOD CONTINUES TO LOOK QUIET. A DRY COLD 
FRONT WILL CROSS THE AREA MONDAY NIGHT FOLLOWED BY HIGH PRESSURE 
BUILDING IN BRIEFLY THROUGH TUESDAY NIGHT. THEN IN THE MID WEEK TIME 
PERIOD...A CLIPPER TYPE LOW WILL DRAG ANOTHER DRY COLD FRONT THROUGH 
THE AREA WEDNESDAY/WEDNESDAY NIGHT. MORE HIGH PRESSURE WILL THEN 
RETURN TO THE AREA THROUGH THE END OF THE PERIOD. TEMPERATURES WILL 
STAY ON THE COOL SIDE FOR THE LONG TERM...WITH HIGHS AND LOWS 
RUNNING SEVERAL DEGREES BELOW CLIMO FOR EARLY JANUARY.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
HIGH PRESSURE TO THE NORTH WILL BE THE INFLUENCING FACTOR AT THE
TERMINALS THROUGH 12Z SATURDAY...KEEPING ANY RISK FOR SHRA TO THE
SOUTH. WHILE WE DO ANTICIPATE VFR CONDITIONS WILL OCCUR...CEILINGS
WILL BE AS LOW AS 3500-6000 FT AT KSAV BUT ABOVE 12K FT AT KCHS.
NORTH-NE WINDS WILL AVERAGE 5-10 KT THROUGHOUT.

EXTENDED AVIATION...INCREASING CHANCES OF MVFR OR LOWER
CIGS/VSBYS SATURDAY EVENING INTO SUNDAY WITH WIDESPREAD SHOWERS
ASSOCIATED WITH A PASSING SURFACE LOW AND COLD FRONT. GUSTY WINDS
AND/OR LOW LEVEL WIND SHEAR ARE POSSIBLE LATE SATURDAY NIGHT INTO
SUNDAY. THERE IS LOW RISK OF TSRA SUNDAY MORNING...MAINLY AT THE
SAV TERMINAL. VFR CONDITIONS WILL RETURN BY LATE SUNDAY THROUGH
MONDAY.

&&

.MARINE...
TODAY AND TONIGHT...A SPRAWLING 1030 MILLIBAR HIGH ALIGNED EAST/NE 
TO WEST/SW WILL COVER A LARGE AREA FROM SOUTH OF NEW ENGLAND TO 
TEXAS...WITH THE LOCAL MARINE COMMUNITY SITUATED NEAR THE SE 
PERIPHERY OF THIS MAIN SYNOPTIC FEATURE. THERE WILL REMAIN A FAIRLY 
DECENT PACKING OF THE ISOBARS BETWEEN THE RIDGE AND A STATIONARY 
FRONT ACROSS EXTREME SOUTH FLORIDA AND THE FLORIDA STRAITS...ENOUGH 
FOR SUSTAINED NORTH AND NE WINDS HOLD FAIRLY STEADY AROUND 15 OR 20 
KT OVER THE ATLANTIC AND 10 OR 15 KT IN CHARLESTON HARBOR. THE WAVE 
SPECTRUM WILL BE COMPRISED OF A MIXTURE OF WIND DRIVEN WAVES AND 
10-11 SECOND SWELLS...PRODUCING SIGNIFICANT WAVE HEIGHTS OF 3-5 FT 
WITHIN 20 NM OF SHORE AND UP TO 6 FT FURTHER OUT. THEREFORE WE HAVE 
MAINTAINED THE ONGOING SMALL CRAFT ADVISORY FOR AMZ374. 

SATURDAY THROUGH TUESDAY...TO START THE PERIOD HIGH PRESSURE WILL 
SIT OFF TO THE NORTH OF THE WATERS AS AN AREA OF LOW PRESSURE 
DEVELOPS OVER THE GULF OF MEXICO. THIS WILL MAINTAIN ELEVATED NE 
FLOW ACROSS THE WATERS IN THE LOCALLY PINCHED GRADIENT INTO SATURDAY 
NIGHT. AS THE LOW TRACKS NORTHEASTWARD SATURDAY NIGHT...A WARM FRONT 
FEATURE WILL LIFT NORTHWARD AS INCREASING SOUTHERLY FLOW SPREADS 
ACROSS THE WATERS. THE FLOW WILL THEN BECOME MORE SOUTHWESTERLY ON 
SUNDAY AND STRENGTHEN THANKS TO A STRONG LOW LEVEL WIND FIELD. 
CONDITIONS WILL THEN LEVEL OFF MONDAY BEFORE A DRY COLD FRONT MOVES 
THROUGH AND BRINGS ABOUT A SHOT OF COOLER AIR AND AN ASSOCIATED 
SURGE. THE SMALL CRAFT ADVISORY FOR THE OUTER GEORGIA WATERS HAS 
BEEN EXTENDED THROUGH SUNDAY NIGHT TO ACCOUNT FOR A COMBINATION OF 
WINDS AND SEAS. ALL OR PARTS OF THE NEARSHORE WATERS AND THE 
CHARLESTON HARBOR WILL LIKELY SEE ADVISORY LEVEL CONDITIONS SUNDAY 
INTO SUNDAY NIGHT...BEFORE IMPROVING ON MONDAY. THE TUESDAY SURGE 
WILL ONCE AGAIN BRING MARGINAL ADVISORY CONDITIONS BACK TO THE LOCAL 
WATERS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 AM EST MONDAY FOR AMZ374.

&&

$$

SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...BSH
AVIATION...
MARINE...